LRUMessageCache.java

/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2013, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.classic.turbo;

import java.util.LinkedHashMap;
import java.util.Map;

/**
 * Clients of this class should only use the  {@link #getMessageCountAndThenIncrement} method. Other methods inherited
 * via LinkedHashMap are not thread safe.
 */
class LRUMessageCache extends LinkedHashMap<String, Integer> {

  private static final long serialVersionUID = 1L;
  final int cacheSize;

  LRUMessageCache(int cacheSize) {
    super((int) (cacheSize * (4.0f / 3)), 0.75f, true);
    if (cacheSize < 1) {
      throw new IllegalArgumentException("Cache size cannot be smaller than 1");
    }
    this.cacheSize = cacheSize;
  }

  int getMessageCountAndThenIncrement(String msg) {
    // don't insert null elements
    if (msg == null) {
      return 0;
    }

    Integer i;
    // LinkedHashMap is not LinkedHashMap. See also LBCLASSIC-255
    synchronized (this) {
      i = super.get(msg);
      if (i == null) {
        i = 0;
      } else {
        i = i + 1;
      }
      super.put(msg, i);
    }
    return i;
  }

  // called indirectly by get() or put() which are already supposed to be
  // called from within a synchronized block
  protected boolean removeEldestEntry(Map.Entry eldest) {
    return (size() > cacheSize);
  }

  @Override
  synchronized public void clear() {
    super.clear();
  }
}